Conventionally, a so-called built-up type XY table actuator utilizing a linear guide has been known as an apparatus for moving an object freely within the XY-plane to perform positioning thereon at an arbitrary position. More specifically, a track rail extending in the X-direction is arranged on a stationary portion such as a bed or a column, and there is provided a lower table moving along this track rail. Further, a track rail extending in the Y-direction is arranged on the lower table, and there is provided an upper table moving along this track rail; and the upper table is moved freely in the X-direction and the Y-direction with respect to the stationary portion. As means for causing the lower table to advance and retreat in the Y-direction with respect to the stationary portion and for causing the upper table to advance and retreat in the X-direction with respect to the lower table, there is known one which converts the rotary motion of a motor to a linear motion by a ball screw and which transmits the linear movement to the lower table or the upper table.
In the XY table actuator constructed as described above, a load of a linear guide device supporting movement of the lower table and the upper table is arbitrarily selected, whereby the XY table actuator is flexibly applicable to various uses from small load uses to large load uses. Further, through appropriate selection of a length of the track rail, it is also possible to elongate a stroke amount of the upper table. However, since the track rail in the Y-direction is arranged on the lower table, which is movable in the X-direction, high rigidity is required of the lower table itself. Further, the height of the XY table actuator as measured from the stationary portion to the upper table cannot but be rather large, resulting in an increase in size and weight of the entire tables.
JP 05-18415 A discloses an XY table in which a reduction in size and weight is achieved through press working of a thin steel plate. More specifically, end portions of steel plates are bent and raised by press working to thereby form a lower plate and an upper plate of a channel-like configuration. Further, there is formed an intermediate plate in which, of its four sides, two opposing sides are bent downwardly and remaining two sides are bent upwardly, with the upper plate, the intermediate plate, and the lower plate being combined with each other such that side wall portions formed by bending are opposed to each other. Balls are arranged between the side wall portions opposed to each other, and the balls roll on the side wall portions, whereby the intermediate plate can move in the X-direction with respect to the lower plate, and the upper plate can move freely in the Y-direction with respect to the intermediate plate. In this XY table, the lower plate and the upper plate may be completely of the same structure although they differ in moving direction with respect to the intermediate plate, thus advantageously helping to achieve a reduction in production cost. Patent Document 1: JP 05-18415 A